Change CCS_OK to EXPECT_CCS.
Now that the flag is set accurately, use it to enforce that the handshake and
CCS synchronization. If EXPECT_CCS is set, enforce that:
(a) No handshake records may be received before ChangeCipherSpec.
(b) There is no pending handshake data at the point EXPECT_CCS is set.
Change-Id: I04b228fe6a7a771cf6600b7d38aa762b2d553f08
Reviewed-on: https://boringssl-review.googlesource.com/1299
Reviewed-by: Adam Langley <agl@google.com>